Smart environments represent the next evolutionary development step in building, utilities, industrial, home, shipboard, and transportation systems automation. Like any sentient organism, the smart environment relies first and foremost on sensory data from the real world. Sensory data comes from multiple sensors of different modalities in distributed locations. The smart environment needs information about its surroundings as well as about its internal workings.
The challenges in the hierarchy of: detecting the relevant quantities, monitoring and collecting the data, assessing and evaluating the information, and performing decision-making and alarm functions are enormous. The information needed by smart environments is provided by Distributed Wireless Sensor Networks, which are responsible for sensing as well as for the first stages of the processing hierarchy. The importance of sensor networks is highlighted by the number of recent initiatives.
Wireless sensors are standard measurement tools equipped with transmitters to convert signals from a control processor into a radio transmission. The radio signal is interpreted by a receiver which then detects the received signal and sends it to a processor to be analyzed. There are a number of items to consider when selecting a wireless measurement instrument.
Type of Measurement: It is important to understand what is being measured. Wireless transmitters (which incorporate wireless process measurement and control) typically have a unique function. Sensors are specifically designed for speed, distance, flow, etc., and must be selected accordingly.
Accuracy and Response Time: How accurate does the measurement need to be, and how quickly should the measurement be updated? Most wireless sensors are as accurate as their wired counterparts; however a signal is typically transmitted frequent enough to allow for accurate measurement while preserving battery power.
Range: The range of wireless sensors varies widely. Some are designed for short-range, indoor applications of a few hundred feet, while other sensors can transmit data to a receiver located miles away. Regardless of the sensors capability, the range of a wireless signal is always limited by obstructions, and frequency of operation. Transmitting through machines, walls, and structures degrades signal strength and reduces range capability. As a result, the range of a transmitter located indoors is typically significantly less than the same transmitter broadcasting outside in wide open field. For certain application very high operating frequency has to be used which limits the operation range.
Frequency: The frequency of radio transmission is also important to consider. Laws vary by country and region as to which parts of the wireless spectrum are available for use without specific licenses. Accuracy and response time in certain application depends on operating frequency, the higher the frequency the more accurate the measurement of certain parameters.
Various components of a wireless sensor system are;
Transmitters: In certain applications the transmitters use particular signals to send via radio waves to a receiver.
Receiver: receives and interpret the wireless data. The receiver ‘reads’ a radio signal, utilize it to estimate and calculate certain parameters, and then send them to a controller to make decision.
Controller: receives and analyze data from wireless receiver. However, the wireless controller is also able to manipulate a process based on the data being measured. For example, if a furnace becomes too hot, a controller can recognize the increased temperature and send a signal to turn off some heating elements.
The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted.